When Joseph P. Galda, a member of the conservative Young Americans for Freedom and of Consumer Alert, enrolled as a Rutgers University freshman here, he was appalled to learn that mandatory fees include $2.50 a semester to support the New Jersey Public Interest Research Group.

Among its other positions, the nonprofit advocacy group – whose establishment in 1972 was inspired by Ralph Nader, the consumer advocate – opposes the expansion of nuclear power and favors abortion rights for women and the proposed Equal Rights Amendment. Mr. Galda opposes the group on these and other issues.

Now a senior who plans to attend law school next year, Mr. Galda is continuing a fight he began as a freshman to change the university policy, which he says requires him to support political and social causes with which he disagrees. A four-day campus referendum on whether the fee should be retained will begin Monday, while the constitutionality of the fee will be tested in the Federal Circuit Court of Appeals in Philadelphia next year.

Counsel for the university have argued in court that the New Jersey Legislature originally endorsed the group’s establishment in the state ”as being in the public interest and in furtherance of the educational mandate of Rutgers.”

Such groups, each incorporated independently since Mr. Nader started the student-advocacy movement in 1972, are active in 26 states, but not all of them are backed by mandatory fees collected for them by the school as part of the semester bill for matriculation, and must depend on voluntary contributions.

Edward Lloyd, executive director of the New Jersey Public Interest Research Group, described the group as a private lobbying organization that actively pursued its interests in social and political issues but did not support political candidates.

Rutgers collects the fee at 11 colleges and schools in New Brunswick, Newark and Camden. The fee has been approved at each by a majority of students voting, with a minimum of 25 percent of the student body favoring it. Students on statewide and campus Public Interest Research Group boards decide which projects to pursue, but opponents say the year-round nonstudent Interest Research Group staff actually guides the decisions and carries out the projects.

At 17 colleges in New York State, the group’s fee is a mandatory part of the student activity fee, while it is separately collected at Rutgers. At the various campuses of Rutgers and the City University of New York, whose governing boards make policy regarding the organization, the fees are refundable to students who do not want to contribute. They are not refundable at campuses of the State University of New York, whose student associations determine whether and to what extent Public Interest Research Groups may draw from student activity funds.

As a freshman, Mr. Galda first complained to Consumer Alert, an organization that opposes ”excessive” government regulation of business and supports freedom of choice for consumers. Barbara Keating, its president, who was the Conservative Party candidate for the Senate from New York in 1974, referred him to the Mid-Atlantic Legal Foundation in Philadelphia.

The foundation is one of six law offices across the country set up since 1975 under the umbrella of the National Legal Center for the Public Interest in Washington. James R. Richards, vice president of the center, said the network’s purpose was to ”provide a balance against extremist environmentalist organizations such as the Sierra Club and consumer-oriented groups such as the Nader organizations.” In 1979, Mid-Atlantic sued Rutgers on behalf of Mr. Galda and two other students, charging that it had unconstitutionally infringed on student free speech and expression by requiring all to contribute.

Last June, Judge Stanley S. Brotman of Federal District Court ruled in Camden that Rutgers students were not, in fact, being compelled to support ideological positions they oppose because they could demand a refund of the fee. The Public Interest Research Group intervened on the side of Rutgers.

Judge Brotman conceded only that ”perhaps it would be preferable if the fee were voluntary rather than mandatory.” Mid-Atlantic appealed to the Circuit Court. In a brief filed Oct. 13, Myrna P. Field, its president, said that since refunds were not made until the end of each semester, ”the fee is in the coffers of PIRG for essentially the entire four scholastic years even if the individual student conscientiously applies for a timely refund on eight separate occasions.”

She said refunding also had the chilling effect of requiring dissenters to identify themselves. ”The funding policy gives one political philosophy an unjustified advantage, the imprimatur of governmental approval,” she said. ”On no occasion has the Supreme Court allowed an entity to collect compulsory fees for political or ideological purposes without the knowing consent of the contributor.”

Because of the controversy over the fee, the student congress at the Camden campus ordered a new referendum on the fee last April. Ordinarily a referendum is held every three years, and the next would have been this fall. The group lost the April referendum, but said it did not campaign because of the time change. It petitioned the college administration for and obtained a substitute referendum for Nov. 16 to 19.

Regardless of the outcome of the referendum here, Mid-Atlantic will pursue its suit. ”We would like the New Jersey case to set a precedent for other PIRGs around the country,” Mrs. Keating said in a telephone interview from Consumer Alert headquarters in Modesto, Calif. ”Some college administrations are awaiting the outcome of this one before taking further action on a future policy on PIRG.”

The New Jersey Public Interest Research Group persuaded Rutgers officials that membership in the group would benefit students educationally by offering them an opportunity to learn about social and political issues and to participate in seeking legislative or other action on the issues.

Frederick L. Whitmer, a Morristown attorney, noted in his brief for Rutgers that the group’s establishment in the state had been endorsed by the New Jersey Legislature ”as being in the public interest and in furtherance of the educational mandate of Rutgers.”

Students may obtain course credit for working on group projects in such fields as consumer and environmental issues, urban revitalization, racial and sexual discrimination, occupational health and safety, tax reform, education and energy policy.

The Rutgers policy, Judge Brotman said, ”advances the two fundamental values underlying the First Amendment: it facilitates individual students’ interests in association and expression and it serves society’s interest in open and informed discussion of public issues.”

Mr. Galda said it provides one-sided discussion and ”accords PIRG an advantage in getting their views across that other campus groups don’t have.” He said that the College Republicans organization he heads raises its own funds, and that the Public Interest Resarch Group should, too.